• Ignition potential of transient sparks produced by abrasive waterjet cutting in explosive environments

      Miller, Hugh B.; Charrier, Erik K.; Steele, John P. H.; Kaunda, Rennie; Nelson, Priscilla P. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Explosive atmospheres are a significant hazard in many mining, mineral processing, and industrial workplaces. These workplaces often require hot work for maintenance, repairs, or production activities. If the workpiece cannot be removed from the potential explosive atmosphere, the hazard must be mitigated through engineering and administrative controls. The hazards must be identified, explosive atmospheres evacuated from the work area, sources of gases removed, and appropriate measure taken to prevent hazards from reentering the area during hot work. Despite these measures, fatalities and significant losses still occur. The ideal solution is to move up the hierarch of controls to substitution.Abrasive waterjet (AWJ) cutting is a potential substitute for hot drilling and cutting processes. At the macroscopic level, AWJ cutting of steel is a cool process. The scientific literature and industry experts have demonstrated that transient sparks can occur during AWJ cutting. No model of AWJ ignition potential is presently available in the literature. The spark generation process and sparks have not been characterized. A single published data set exists with ignitions reported at 300MPa (43.5kpsi) and is not representative of field cutting parameters that represent a potential hot work substitute.The AWJ ignition process was characterized and a model of AWJ ignition was developed. Energy transfer and spark generation were calculated from the model and the maximum potential spark was characterized. Based on the model, it was hypothesized that reducing the operating pressure would reduce the ignition rate. Experiments were conducted with AWJ parameters representative of field cutting applications. Drilling and linear cutting tests were conducted at 69MPa (10kpsi) in a hydrogen-oxygen atmosphere. No ignitions occurred during the drilling and cutting experiments. It is concluded that AWJ cutting is a promising potential hot work substitute for cutting and drilling steel in a subset of explosive atmospheres. Further parametric analysis is recommended.
    • Data-driven approach to calculating nodal net load forecasts in power systems analysis, A

      Sen, Pankaj K.; Zhang, Yingchen; Ausmus, Jason R.; Wang, Hua; Simões, M. Godoy; Ammerman, Ravel F.; Krishnan, Venkat (Colorado School of Mines. Arthur Lakes Library, 2020)
      The electric power grid is one of the largest and most complex systems ever built for the benefits of humanity. Most of the modern world relies heavily upon this system, and its unavailability may result in severe economic, safety, and security issues. Ensuring the electric power grid maintains an adequate level of reliability is a challenging task that usually begins well in advance of real-time system operations. This task of ensuring grid reliability typically begins in system operations with the Operational Planning Analysis (OPA). TheOPA is a study required by the North American Electric Corporation (NERC) Reliability Standards. The goal of that study is to assess whether planned operations for the next day will exceed any operating limits or present any potential reliability threats to the system. The next day is also the same time frame in which the electricity markets begin to procure resources needed to meet the following day's demand or forecasted load. The foundation for these studies is the load forecast. The accuracy of it can determine the next day's system requirements, e.g., generation and system outages. The problem is that the load forecast is typically done at the system level, and for power system engineers, the accuracy of the data is needed at the most granular level, the load bus. A bus or node level forecast does not exist in the industry today, and this research aims to develop a method based on the historical data accumulated by the utility companies. This research also describes the concept of net load, which is the resultant value of load and resources real-time system operators monitor at the transmission system level. This dissertation discusses the current practice of the utilization of load forecast data in the electric utility industry. It proposes a new data-driven framework based on machine learning to predict net loads at the node or bus level.
    • Development of II-VI ternary alloys for CdTe-based solar cells

      Wolden, Colin Andrew; Samoilenko, Yegor Yurevich; Agarwal, Sumit; Carreon, Moises A.; Ohno, Timothy R. (Colorado School of Mines. Arthur Lakes Library, 2020)
      CdTe has emerged as the leading commercial thin film photovoltaic technology. Recent advancements in photoconversion efficiency were achieved through the introduction of alloyed CdSeyTe1-y (CST) absorber, as well as replacement of conventional CdS window layer with more transparent alternatives such as MgxZn1-xO (MZO). These II-VI ternary alloys offer a wide range flexibility of adjusting several important parameters of the CdTe-based solar cells, such as band gap and conduction band alignment. The focus of this thesis can be divided into two parts: development of Cd1-xZnxTe (CZT) absorbers and combinatorial discovery of MZO emitters.CZT alloys form at the back of the device stack during back contact activation by interdiffusion between CdTe and ZnTe. ZnTe doped with Cu is commonly used as a buffer layer at the back of the device stack to facilitate creation of an ohmic contact with CdTe absorber. In addition, Cu diffuses into CdTe and provides p-type doping for the absorber. The role of Cu during back contact activation was studied in this thesis. By depositing bilayers of CdTe and ZnTe:Cu with varying Cu loadings and subjecting them to short annealing steps it was shown that Cu is a critical flux agent that induces interdiffusion, recrystallization, and grain growth in a matter of minutes at studied temperatures of 320 oC and above. Cu was also shown to scavenge excess Te in ZnTe to form CuxTe clusters. CZT alloys are also of interest as absorber due to the full miscibility of CdTe and ZnTe that enables a tunable band gap from 1.5 to 2.26 eV. In particular, CZT alloys with a band gap of ~1.7 eV can potentially be used as a top cell in a tandem device. However, conventional device processing, specifically the CdCl2 activation step, results in the loss of Zn and the formation of stacking faults. We explored the use of molecular Cl2 to improve stability of CZT alloys during device processing. In comparison to conventional CdCl2, the use of molecular Cl2 offers an advantage of independent control of temperature and Cl2 concentration. Cl2 concentration of 15 ppm was identified to eliminate Zn loss at temperatures equivalent to conventional CdCl2 treatment, i.e. 400-450 oC, however, photoluminescence measurements revealed minimal increase in the signal, suggesting incomplete activation of the absorber material. Cross-sectional transmission electron microscopy revealed accumulation of chlorine on top of the absorber but no chlorine was seen inside the bulk of the absorber or at the grain boundaries, which is most likely the reason for the poor activation of the absorber.MZO emitters are significantly better than conventional CdS due to their transparency and tunable conduction band alignment with CdTe or CST absorber. MZO is most commonly deposited by sputtering using pre-formed ceramic targets of fixed composition in an Ar ambient. This limits one to discrete compositions and is expensive. In addition, the stability of MZO has been a concern. The MZO stability issue has been attributed to the presence of oxygen in the CdTe device processing ambient, leading to double-diode behavior (S-kink) in the current density-voltage curves. Reactive co-sputtering technique from elemental Zn and Mg targets in Ar:O2 ambient developed in this work offers an alternative to conventionally prepared MZO. Reactive co-sputtering produced high quality, robust MZO films with promising stability and resilience to processing conditions. This stability of reactively co-sputtered MZO is attributed to be due to low concentrations of oxygen vacancies in the films, which was confirmed by electrical and Kelvin probe measurements. The “ideal” MZO composition depends on the specific architecture and processing employed. The combinatorial approach enabled rapid identification of optimal composition, as evidenced by achievement of high performing devices (~16%) across multiple research facilities both with and without oxygen in device processing ambients.
    • Predicting mining company-stakeholder conflict and incorporating social conditions into mining project valuation

      Holley, Elizabeth A.; Teschner, Benjamin Augustus; Düzgün, H. Sebnem; Brune, Jürgen F.; Smith, Nicole M.; Santi, Paul M. (Paul Michael), 1964-; Wilson, William (Colorado School of Mines. Arthur Lakes Library, 2020)
      External stakeholders are becoming increasingly involved in mine design and permitting decision-making. Yet, the systems in which mining investment decisions take place do not fully capture the importance of stakeholder influence on the success or failure of a mining venture. Conventional mine planning and permitting methods elevate technical expertise, conventional views of risk management, and financial justifications as the drivers of “objective” decision making. The rising influence of external stakeholders to mining project outcomes means that stakeholder attitudes on mining, and institutional trust, and local environmental knowledge must be integrated into the decision-making systems in more comprehensive ways. This dissertation is a compilation of three research papers which seek to answer the following research questions: 1. How can governments better integrate local communities’ perceptions and concerns into mine permitting decisions? 2. What are the most important indicators of company-stakeholder conflict?3. How does stakeholder opposition affect the valuation of a mining property?This dissertation informs these questions with three research activities: A case study of the National Environmental Policy Act (NEPA) at the Donlin Gold project in Western Alaska: The National Environmental Policy Act requires US regulators to consult local stakeholders and include their concerns in an Environmental Impact Statement (EIS). At the Donlin project in Western Alaska, the Army Corps of Engineers included Alaskan Native tribes as cooperating agencies in the analysis in addition to conventional public comment meeting. This attempt at improved stakeholder involvement had some successes, but it also highlights divergent goals within NEPA and a lack of trust between local stakeholders and regulators. Tribes were able to push for examination and disclosure of some of their environmental concerns but remain frustrated with NEPA’s limitations with respect to transform findings into enforceable protections.A statistical examination of the social and environmental variables as indicators of company-stakeholder conflict: Prediction of company-stakeholder conflict remains a weak point in mine design and planning. This research statistically examines a database of mining properties and develops multiple linear regression models to identify the most important indicators of mining company-stakeholder conflict. These models find that the following conditions are the strongest indicators of future conflict: the conflict history of the mining property, the conflict history in the mining region, proximity to artisanal mining, and anticipated physical and economic displacement of local people.A decision tree model which incorporates company-stakeholder conflict into a mining project’s valuation: Mining investment decisions rely on a company’s financial valuation of a mining project. The discounted cash flow methodology is the foundation of these valuations. This research developed a tool for capturing the financial risk associated with higher likelihoods of company-stakeholder conflict by quantifying the risk of forced project abandonment. This research presents a decision tree model for calculating the expected cost of company-stakeholder conflict. The model concludes that even moderate conflict likelihoods can reduce the net present value (NPV) of a mining project by hundreds of millions of dollars. Collectively these studies conclude that external stakeholders are undervalued by mining’s present decision-making paradigms. This dissertation calls on companies and governments to place a greater emphasis on external stakeholders’ perspectives on mining. It recommends that companies and governments engage these stakeholders in permitting and mine design processes such that these decisions include nuanced understandings of how a mine will affect local people and how local people will affect a mine.
    • Protonic ceramics for electrochemical hydrogen compression

      DeCaluwe, Steven C.; Kee, Benjamin Lyons; Ricote, Sandrine; Porter, Jason M.; O'Hayre, Ryan P. (Colorado School of Mines. Arthur Lakes Library, 2020)
      The topic of this thesis is designing and characterizing protonic ceramics for the electrochemical hydrogen compression. Protonic-ceramic reactors are attractive for compressed hydrogen production from natural gas because they can effectively integrate steam reforming, hydrogen separation, and electrochemical compression. The current technology requires many unit processes, which introduces significant inefficiency. This thesis first explores protonic-ceramic electrochemical hydrogen compression on tubular cells. Compression to 10 bar was demonstrated, but progress was limited by material availability and scale-up opportunities. A method was developed to fabricate protonic-ceramic cells. The easily-produced samples were characterized and modeled. Discs were made for planar stack development to investigate sealing and reactor design strategies. Scaling up protonic-ceramic electrochemical hydrogen compression is an ongoing challenge. Experiments with tubular cells have compressed H2 up to 10 bar. Tubes are ideal for heavy compression due to strong hoop stress resistance, which is applied from the pressure difference during compression. Unfortunately, tubular geometries do not lend themselves well to stacking, due to poor electrode connections and footprint size. The scarcity and poor compatibility of tubular cells create an opening for new methods to make protonic-ceramic cells. The polymer clay method is a novel processing technique for moldable ceramics in the green state, that fire completely dense. Herein, fabrication of protonic-ceramic membranes is demonstrated in a variety of shapes. Conductivity relaxation measurements between moist and dry reducing conditions on polymer clay coupons were collected and fit to an ambipolar diffusion model. Results demonstrate that polymer clay samples are competitive to samples made by other methods. The final topic of this thesis is how to incorporate efficient cells in robust and durable stacks for electrochemical H2 compression. Planar stack configurations have been heavily explored with other electrochemical devices, including fuel cells. Planar geometries are more conducive to stacking and have tightly integrated electrode connections. Sealing strategies between the bipolar plate and the membrane electrode assembly were explored to determine best practices. Our results demonstrate hydrogen pumping on single cells. While hermetic seals for planar cell stacking remain an ongoing area of study, this study identifies potential solutions.
    • High temperature broadband microwave absorbing materials

      Brennecka, Geoffrey; Leppert, Megan M.; Nayeri, Payam; Gorman, Brian P.; Reimanis, Ivar E. (Ivar Edmund) (Colorado School of Mines. Arthur Lakes Library, 2020)
      Advancements in military and aerospace applications have increased the demand for high temperature microwave absorbing materials. While current state of the art composite material solutions contain strong absorption capabilities, they fail to perform in harsh thermal environments due to thermal limitations of the composite matrix. This work focused on fabricating a ferroelectric-ferrite ceramic composite capable of absorbing electromagnetic energy across a wide range of frequencies and temperatures. The dielectric properties of A-site non-stoichiometric sodium bismuth titanate (NBT) were investigated to determine if electrical losses could be tailored by altering the Na to Bi ratio. A bismuth deficient composition resulted in two electrical loss mechanisms at temperatures above 200°C associated with oxygen ion mobility and polaron hopping between Ti4+ and Ti3+. Nickel zinc ferrite (NZF) was selected as the second composite component for the flexibility it provided in both dielectric and magnetic properties based on composition and processing conditions. Highly conductive grains and resistive grain boundaries, attributed to electron hopping between Fe3+ and Fe2+ led to an electrical loss mechanism at temperatures up to 400°C. The magnetic and dielectric properties of composite samples xNZF + (1-x)NBT were evaluated at elevated temperatures and frequencies up to 1 MHz to determine the impact the two phase composite solution had on the individual properties of NBT and NZF. Three distinct thermally activated loss mechanisms were present in the composite samples leading to broadband absorption across the test frequencies of 1 kHz to 1 MHz and temperatures up to 600°C. Transmission and reflection data from X- and Ku-band rectangular waveguides (8-18 GHz) were used to evaluate the magnetic and dielectric properties of the composite samples at room temperature. xNZF + (1-x)NBT composites demonstrated significant attenuation across the microwave frequencies tested. The microwave absorbing capabilities of xNZF + (1-x)NBT composites at elevated temperatures were extrapolated by combining the thermally activated loss mechanisms studied at frequencies below 1 MHz, with room temperature electromagnetic properties collected at 8-18 GHz.
    • Multi-pass cross-polarized wave generation system for efficient cleaning and compression of ultrafast pulses

      Durfee, Charles G.; Byrne, Dominic M.; Adams, Daniel; Squier, Jeff A. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Cross polarized wave generation (XPW) is an effect that occurs in crystals that have an asymmetric third-order nonlinear susceptibility. Because of the cubic intensity dependence of the conversion efficiency, the XPW pulse is shorter in time than the input pulse. For well-compressed pulses, the XPW spectrum will be broader and the temporal profile is cleaner, with better contrast between the pulse peak and the low-intensity background. Shorter, cleaner pulses are desirable for many applications. An example of an application for cleaner pulses like this is for experiments where high intensity pulses hit solid targets. Having better intensity contrast between the pre-pulse and the main pulse allows the main pulse to interact with the unexpanded, high density plasma. In this thesis, a novel method is developed to improve conversion efficiency that should also provide better quality spatial modes than previous methods. An optical system was demonstrated where the pulse is relay-imaged from the crystal to itself for multiple passes. This system allows for efficient conversion of low intensity pulses (low energy or long duration). Also, since chirped mirrors can be placed in the setup, the pulse can be more efficiently compressed to short duration. Conversion efficiencies as good as some previous improvement methods are achieved while using uncoated crystals, with quality output mode shapes. Using anti-reflection coated crystals with this new multiple pass setup will likely lead to significant improvement in conversion efficiencies. This method will be attractive for high repetition rate amplified systems that have modest pulse energy in the microjoule range.
    • Isolated high efficiency multiplier cell-based PV system DC-DC converter for residential applications, An

      Simões, M. Godoy; Alsaleem, Abdulhakeem; Arkadan, Abd A.; Han, Qi; Sen, Pankaj K. (Colorado School of Mines. Arthur Lakes Library, 2020)
      The global increase in PV installations has driven researchers to find more efficient integration techniques for interfacing PVs with the grid. More innovative converter structures are required to overcome the challenges that face conventional converters. This research presents a high voltage gain isolated DC-DC converter that is suitable for PV applications. The novel converter utilizes a high frequency transformer with 1:1 turns’ ratio and multiplier cells that are also utilizing a 1:1 high frequency transformer. This new approach in topology fabrication allows for a reduced component rating and a very low normalized switch voltage ratio. That means very high voltage gain converters can be realized by using very low voltage switches and diodes. In addition, 1:1 turns’ ratio transformers are easier to design and simpler to manufacture and cut the required duty cycle to half if used in half or full bridge configuration. This research also presents the designed non isolated DC-DC converters that led to the realization of the isolated DC-DC converter. A 450 W prototype is presented and tested to validate the concept and an efficiency study for the converter is also presented.
    • Solubility characteristics of luminescent materials for organic light emitting diodes

      Zimmerman, Jeramy D.; Bales, Joseph R.; Collins, Reuben T.; Furtak, Thomas E. (Thomas Elton), 1949- (Colorado School of Mines. Arthur Lakes Library, 2020)
      Organic light emitting diodes (OLED’s) have the potential to be as efficient as inorganic LED’s but significantly cheaper to fabricate. Before these devices can be considered as complete replacements for LED’s, some problems with efficiency loss and degradation must be addressed. Here, we intend to address phase separation and problems it exacerbates,such as triplet-triplet annihilation and polaron-triplet quenching. We hope to address phase separation through manipulation of the solubility properties of the OLED emissive layer materials. We use Hansen Solubility Parameters, which describe solubility for materials in such a way that we can determine the best solvent for a given solute. The current tests for these parameters are not practical for these materials, so we have developed a new procedure for measuring the solubility properties of luminescent materials and used this procedure to test four common OLED materials. The data these tests produced is not precise enough at this time to draw any definitive conclusions about these materials’ solid-solubility.
    • Laboratory study of the effect of chemical osmosis on the elastic rock properties of Pierre shale and implication for oil recovery

      Tutuncu, Azra; Kazemi, Hossein; Adekunle, Olawale O.; Ozkan, E.; Sonnenberg, Stephen A.; Katsuki, Daisuke; Yin, Xiaolong; Trudgill, Bruce, 1964- (Colorado School of Mines. Arthur Lakes Library, 2020)
      The main objective of this research is to experimentally (1) measure the effect of chemical osmosis on elastic properties of shale, (2) determine chemical osmosis membrane efficiency under in-situ stress, and (3) evaluate the swelling tendency of Pierre shale resulting from chemical osmosis and its implication on oil production. Three relevant tri-axial experiments were conducted on Pierre shale core samples, before and after fluid invasion at reservoir pressure and temperature conditions, to determine rock properties and behavior. To accomplish the tasks, a new tri-axial cell was built to accommodate coupled acoustic and static measurements attributed to swelling during water intrusion into the Pierre shale matrix. Bulk modulus, Poisson's ratio, and shear failure envelope of Pierre shale were determined from measurements on several shale samples with varying clay content. The membrane efficiency of the shale samples was experimentally determined to be in the range of 10 to 30% depending on clay content and stress level. Swelling strains of the samples were determined from experiments to be 1% in high smectite content samples and 0.07% in a 3.5 wt.% TOC sample from Pierre shale. For the PI-LC-WY-H-01 Pierre shale sample with low smectite and high TOC, we obtained an internal friction angle of 48.4 degrees. The shale samples containing high swelling clays indicated a decreasing trend in Young's modulus when low salinity brine imbibed into the pore space by chemical osmosis. For relatively low smectite content and high TOC, the Young’s modulus increased when water saturation increased during osmosis pressure build-up. The aforementioned results were included in the numerical model to account for osmosis and clay swelling characteristics on oil recovery from the rock matrix. The correlation of the membrane efficiency with stress is dependent on the formation mineralogy, particularly clay content. A coupled mass transport-geomechanical mathematical model was developed (1) to simulate mass transport between the fracture and rock matrix amidst the occurrence of clay swelling, and (2) to evaluate how fluid and rock interactions could affect oil recovery from the rock matrix in unconventional reservoirs. The model was used to evaluate oil recovery from a single matrix block while accounting for the change of membrane efficiency with stress, swelling, and mechanical property of shales. Based on our laboratory observations, I recommend investigating the swelling tendencies of shale formations before any water injection operations, especially for low salinity water injection. I also recommend determining the increase in effective stress with clay content resulting from low salinity water injection.
    • Multiscale modeling of the lumbar spine to investigate tissue-level load transfer during activities of daily living

      Petrella, Anthony J.; Honegger, Jasmin D.; Silverman, Anne K.; Berger, John R.; Munson, Ashlyn (Colorado School of Mines. Arthur Lakes Library, 2020)
      The prevalence of low back pain (LBP) in certain subpopulations who experience more extreme repetitive spine kinematics is often attributed to biomechanical factors. Repetitive loading of the spine during lumbar movements produces damage in innervated elements known to be sources of pain, with examples including: vertebral body fractures, intervertebral disc tears, endplate lesions, and abnormal disc stress. Thus, understanding how lumbar spine kinematics influence load transfer within the tissues during daily activities can provide insight into determining how population-specific biomechanical LBP develops. Methods used to directly measure lumbar spinal loads in vivo and in vitro can be highly invasive, are not always measured in living humans, and are often not measured during daily activities. Computational modeling techniques provide a solution in silico for estimating lumbar spinal loads that are difficult or impossible to measure. While common types of biomechanical computational models (i.e., musculoskeletal and finite element (FE) models) have many benefits, they are limited when employed separately. Multiscale modeling involves combining two or more computational models into a single framework to leverage their capabilities and enable estimation of tissue loads driven by physiological kinematics and loading. This research sought to address the need for a computational model of the lumbar spine to estimate tissue-level load transfer driven by in vivo kinematics for people who are prone to developing biomechanical LBP. In this body of work, a multiscale model of the lumbar spine (musculoskeletal + FE) was developed, validated, and applied clinically. The model was validated against in vitro torque-rotation and force-displacement responses, as well as in vivo intradiscal pressure. The model was applied to people with and without a transtibial amputation (TTA) to assess differences in tissue load distribution during daily activities between groups. Lumbar spine tissue loads were also analyzed for a participant with a TTA and LBP who underwent movement retraining rehabilitation to investigate if the multiscale model can help to corroborate clinical decision making. A design of experiments was performed to determine normal variation in the model and it’s relation to clinical relevance, as well as technical modeling implications for predicting tissue loads from physiological kinematics and kinetics. The overarching goal of this research was to lay the groundwork for developing a computational model that can be adapted for use with different populations, pathologies, geometries, and activities and can be used in parallel with treatment protocols towards improved patient-specific care of biomechanical LBP.
    • Experimental study of tunnels in squeezing ground conditions

      Gutierrez, Marte S.; Hedayat, Ahmadreza; Arora, Ketan; Zhou, Wendy; Pei, Shiling; Düzgün, H. Sebnem; Hampton, Jesse Clay (Colorado School of Mines. Arthur Lakes Library, 2020)
      The presence of squeezing ground conditions often poses significant challenges in predicting tunnel response over time and to the design of an adequate support system to stabilize the tunnel. Over the years, many methodologies have been proposed to predict squeezing in tunnels based on tunnel depth, in situ stress, ground mineralogy, and ground strength and deformation behavior. Most of these methodologies are problem-specific and limited in scope. The study presented in this thesis was focused on improving the understanding of tunnel squeezing via a unique physical model test that simulated tunnel boring machine (TBM). To identify the critical parameters contributing towards squeezing, a case study of four tunnels constructed in squeezing clay-rich rock was carried out. It was established from the case studies that by combining normalized engineering behavior of rocks, Peck’s stability number and Geological Strength Index (GSI), the squeezing potential for the tunnels could be determined. A squeezing number S is suggested to classify ground conditions based on the level of squeezing that the ground may experience in response to tunneling. It was demonstrated that by combining the proposed classification system and an existing classification system for squeezing ground conditions, an accurate estimate of tunnel strain could also be obtained. Following the case studies, a novel physical model test to simulate a tunnel boring machine (TBM) excavation in squeezing ground conditions has been proposed. The physical model included a large true-triaxial cell, a miniature tunnel boring machine (TBM), a laboratory-prepared synthetic test specimen having properties similar to natural mudstone, and instrumentations to monitor deformations around the tunnel boundary during and after the excavation. The true-triaxial cell can apply principal stresses up to 13 MPa on a 300x300x300mm3 cubical rock specimen independently on the three principal planes, and this corresponds to real in-situ stress conditions. Miniature TBM can excavate a tunnel having 48-mm and maximum length 150-mm. The instrumentation and monitoring included embedded strain gauges in the form of multiple point borehole extensometer (MPBEx) and a caliper to monitor deformations around and at the tunnel boundary, respectively. The preliminary testing showed the capability of the test setup in capturing crucial features of tunnel excavation, such as tunnel advance, three-dimensional effects, and highly plastic and ductile time-dependent behavior of the ground. The physical model was used to study the behavior of supported and unsupported tunnels at various isotropic stress levels. The deformation data were obtained from the embedded strain gauges, digital borehole caliper and strain gauges on the support system. The degree of tunnel squeezing was characterized using a classification system based on tunnel radial strain. A model for time-dependent tunnel longitudinal displacement profile (LDP) for unsupported and supported tunnels was proposed using measurements of the tunnel convergence at different times and different stress levels. The LDP parameters for both the cases were compared to account for the influence of the support system. The back-calculation of thrust forces on the support system provided an estimate of the additional effects induced in the support due to squeezing. Finally, based on the observations, a recommendation for the analysis to determine safe and economical support for the tunnel constructed in squeezing ground was proposed.
    • Enhancing socio-technical integration of remediation efforts in artisanal and small-scale gold mining communities

      Smits, Kathleen M.; Smith, Nicole M.; O'Brien, Rosalie M.; Phelan, Thomas J.; Munakata Marr, Junko (Colorado School of Mines. Arthur Lakes Library, 2020)
      Artisanal and small-scale gold mining represents the largest source of anthropogenic mercury contamination in the world, creating long-term exposure risks to miners and communities in which these operations exist. Eliminating these health and environmental risks requires the implementation of remediation projects in coordination with local communities. Yet, current remediation frameworks lack thorough guidance on integrating local knowledge with technical data, and projects therefore emphasize technical forms of knowledge over local knowledge. This research bridges this gap by first analyzing previous remediation projects in developing countries. The review concluded that stakeholder engagement leads to greater project success by enhancing communication and creating project goals that meet the needs of different stakeholders. Yet, stakeholder engagement with a diverse range of individuals and organizations is not pursued by the majority of remediation projects. This critical need for stakeholder engagement led to the redevelopment of a common decision-making tool in remediation: the conceptual site model. During a field visit to an ASGM community in Antioquia, Colombia, three iterations of preliminary conceptual site models were created by integrating ethnographic research methods and existing technical information. The framework for creating community-informed conceptual site models further offers opportunities for engineering students to engage with stakeholder engagement within site remediation course curriculum, thereby equipping students to solve complex engineering problems prior to entering their professional career. The culmination of this research presents a comprehensive reform of the engineering discipline within remediation by exposing opportunities for local knowledge to enhance remedial endeavors and offering methods for incorporating local knowledge directly into remediation projects.
    • Contextualizing and communicating the ancillary benefits of green stormwater infrastructure

      Hogue, Terri S.; McCray, John E.; Spahr, Katie M.; Smith, Jessica, 1980-; Munakata Marr, Junko; Higgins, Christopher P.; Stokes-Draut, Jennifer (Colorado School of Mines. Arthur Lakes Library, 2020)
      As we move into an era of increased urbanization, stormwater practitioners are charged with creating multi-functional solutions through the installation of stormwater control measures (SCMs). Green stormwater infrastructure (GSI) mirrors natural hydrologic processes and can be used as an alternative or complement to traditional grey infrastructure. To encourage greener interventions, practitioners promote co-benefits (ancillary social, ecological and environmental outcomes). Co-benefits are difficult to quantify because they span a diverse set of categories that cannot be easily measured with a single metric. This dissertation advances the science of co-benefits by querying (1) the impact greening programs have on vegetation in cities, (2) the public’s preference for GSI and co-benefits, and (3) the feasibility of incorporating co-benefits into the planning process. First, a ten-city greenness study found that robust GSI programs did not always correspond with increased city-wide greenness. In Philadelphia, the installation of non-vegetated SCMs contributed to decreased urban greenness. Second, a survey administered in three cities found that respondents preferred new GSI installations and had less confidence in GSI to handle storms. The co-benefits surveyed were favorable to most respondents, but a clear divide was identified between environmental and socio-economic related benefits. Finally, a critical review of the literature informed a SCM/benefit attribution matrix that was then applied to a case study in the Berkeley neighborhood of Denver, CO. We found that hydrologic benefits related to SCMs can be quantified using stormwater modeling. To assess vegetated benefits related to SCMs, we created the framework of the 4 C’s (community, context, connectivity and canopy) to leverage surrounding urban green infrastructure (like parks) because the modeled solution would add only 1% to the neighborhood’s vegetated area. To incorporate the results of this dissertation into stormwater planning, we advocate that municipalities adopt multi-department integrated vegetation goals to optimize the benefits of all types of urban green infrastructure.
    • Petroleum exploration in the mature Phitsanulok Basin, Thailand: success and failure analysis, and characterization of source rocks and crude oils

      Milkov, Alexei V.; Noosri, Ratthapon; Sonnenberg, Stephen A.; Trudgill, Bruce, 1964- (Colorado School of Mines. Arthur Lakes Library, 2020)
      Finding new petroleum resources is one of the important tasks to sustain the future of energy consumption. Considerable petroleum resources can be added through exploration in frontier and emerging basins and plays. However, finding petroleum accumulations and proving new exploration concepts in the maturing and mature areas are also essential to prolong the consumption of energy from fossil fuels. The study area for this thesis is located in the Sirikit Oil Field, the Phitsanulok Basin, Northern Thailand. Sirikit Oil Filed has been explored and produced for almost 40 years. During all those times, PTTEP (the national petroleum exploration and production company based in Thailand) has performed several types of activities attempting to prolong the field life. Although there were several exploration campaigns to locate additional resources, especially in the eastern part of the Phitsanulok Basin in the past ten years, the success rate of the exploration wells is quite low. The objective of the thesis was to study the petroleum system and define additional petroleum potential of failure areas using post-mortem analysis and source rocks-crude oils characterization. The success and failure analysis indicates that the most common critical failure mode of the Eastern Flank area is the migration, especially in the most eastern part of the study area. This area might fail because of a great distance away from the kitchen area, limiting lateral hydrocarbon migration to the particular region. Characterization of source rocks and crude oils presents two source rocks facies in the Phitsanulok Basin, including lacustrine and terrestrial facies. These two source facies are located in different areas and charged petroleum into different regions. Lacustrine source facie is dominated by Type I kerogen, situated in the Sukhothai Depression and the south of the Basin. This source rock facie mainly charged hydrocarbon to the southern part of the Basin. On the contrary, terrestrial source facie mainly consists of Type III kerogen type and dominated in the Sukhothai Depression and the eastern part of the basin. Petroleum generated from the latter facie mostly migrated to the Eastern Flank area. Expected source rocks in both discovery and failed exploration areas are in an immature stage of the oil generation window. Therefore, hydrocarbons present in the successful area is migrated from the mature terrestrial facie from the kitchen area or mature local sources nearby. All of the results indicate that potential areas for future exploration activities are located in between proven hydrocarbon migration boundaries and none hydrocarbon show lines, especially in the Pratu Tao and the Lan Krabu plays.
    • Effect of fluid viscosity and density on proppant transport in complex slot systems, The

      Miskimins, Jennifer L.; Bahri, Ashtiwi; Yin, Xiaolong; Ermila, Mansur A. (Colorado School of Mines. Arthur Lakes Library, 2020)
      The main functions of hydraulic fracturing fluids are to create a fracture network and to carry and place the proppant into the created fractures networks, thus, keeping the fractures open and allowing hydrocarbons to flow from the reservoir into the wellbore. Many studies have been performed over the years to develop an ideal fracturing fluid system. Development focus has generally been on optimization of a fluid rheology that can carry and place the proppant into the created fractures with less damage to the formation and at a lower cost. The main goal of this research is to continue building the understanding and optimization of proppant transport in a complex hydraulic fracture network. Specifically for this research focus is placed on two different fluids, water-glycerin solution and water-sodium chloride solution, representing varying density and viscosity. The effects of changing fluid viscosities, densities, proppant densities, proppant sizes, proppant concentrations, and slurry injection rates on proppant transport were then investigated. This experimental work was performed using a laboratory size slot apparatus at the Colorado School of Mines. Four different proppants were tested, 100 mesh sand (2.65 sp.gr), 40/70 mesh sand (2.65 sp.gr), 40/70 mesh ceramic (2.08 sp.gr), and 40/70 mesh ceramic (2.71 sp.gr), at two slurry injection rates (1 and 2 gal/min) and two proppant concentrations (1 ppg (Cv=0.043) and 2 ppg (Cv=0.086)). Also, this study reviews the published correlations for proppant dune height and compares the calculated results with the lab results. The experimental results show that a water glycerin solution (viscosity of 4.3 cp) has a better capability of carrying the proppant into farther locations and to greater distances, which was ascertained by the weight of the collected proppant out of the sampling points. On the other hand, the results show that water-sodium chloride solution of 9.24 ppg density has less capability to carry the proppant deep into the fractures. The results also show that the proppant covered area inside all of the farther fractures (T-1, S-3, and T-2) from the injection point was greater using the water-glycerin solution that the water-sodium chloride solution, due to the ability of the high viscosity to keep more proppant suspended. For all tested proppants, the results show that increasing fluid density had no significant effect on the equilibrium dune height and proppant travel distance. Moreover, the results show that increasing the number of injected particles has a similar effect as that of increasing proppant concentration, both situations leading to quick dune build-up rates and increased proppant covered areas. For both tested fluids, the results show that increasing the injection rate has a significant impact on proppant transport. As the injection rate increases, the proppant dune height decreases and both the proppant covered area and the proppant collected from sampling points increase as well. It was found that smaller proppant sizes such as (100 mesh sand) transported deep into the slot system with lower dune height, as compared with larger proppant sizes (40/70 mesh). Also the results show that proppant density has a significant impact on proppant transport. Decreasing the proppant density resulted in increasing the proppant covered area inside the slots. This experimental work shows that viscosity has a greater impact on the proppant transport than fluid density does, thus implying a larger impact on the resulting fracture conductivity. All of the lab data were compared to published correlations that can predict proppant dune height inside the main fracture by Wang et al. (2003) and Alotaibi and Miskimins (2015). Both correlations showed values close to the laboratory measured values with some minor (< 2.5%) average percent difference. Overall, it appears that these correlations can be used to predict the equilibrium dune height inside the main fracture with low error values and without adjusting any parameters for the tested systems.
    • Deep learning methods for shear log predictions in the Volve field Norwegian North Sea

      Prasad, Manika; Al Ghaithi, Aun; Zerpa, Luis E.; Behura, Jyoti; Wang, Hua (Colorado School of Mines. Arthur Lakes Library, 2020)
      Shear logs are required to calculate reservoir characterization or geomechanics parameters. Shear logs are also used for various seismic analysis applications, such as Amplitude Versus Offset (AVO) inversion and multicomponent seismic interpretation. Furthermore, shear logs or their inverse shear velocity logs are an essential component for rock physics analysis in order to constrain seismic inversion results for potential reservoir pay intervals, in reservoir characterization practices. Often, shear logs are missing to reduce well logging costs, or the data are of poor quality due to poor borehole conditions, or cycle-skipping. This thesis discusses artificial neural networks (ANNs) for shear log predictions using data from the Volve field, in the Norwegian North Sea. In this thesis I use deep neural networks or feedforward neural networks, and I propose convolutional neural networks and recurrent neural networks, to predict shear logs from gamma ray, bulk density, neutron porosity, true formation resistivity, compressional sonic and depth logs. Multiple efforts have been made to predict shear logs using machine learning methods. These studies mostly used one well each for training data and for blind testing. To the best of my knowledge, a comprehensive study that includes well logs, including shear data, from multiple wells in a single field to synthesize shear logs using machine learning methods is lacking. In this thesis I explore the robustness of deep learning methods for shear log (DTS) prediction, using a quantitative measure of accuracy scoring for prediction, such as the coefficient of determination R-squared, and the Root Mean Squared Error (RMSE), using six wells that contained DTS data. I use deep learning methods to synthesize shear logs using all wells with shear log data in the Volve field, Norwegian North Sea. This thesis will provide geoscientists with a tested deep learning approach to synthesize shear logs on a full field scale data set, and to assist in shear prediction for reservoir characterization applications such as AVO inversion, or geomechanical parameters calculation such as shear modulus.
    • Cost effectiveness of beam-column gravity systems for mass timber buildings

      Pei, Shiling; Chaggaris, Rachel; Liu, Hongyan; Kingsley, Gregory (Colorado School of Mines. Arthur Lakes Library, 2020)
      Mass timber construction (MTC) has grown in popularity in recent decades, leading to the adoption of new construction types for MTC to be included in the 2021 International Building Code (IBC). Estimating the cost of mass timber construction is uniquely different and less understood than the cost estimation of concrete, steel, and light-framed wood buildings. This thesis will provide a better understanding of cost estimation of mass timber construction by investigating the cost sensitivity of key design features for a mass timber gravity system. An algorithm consisting of automated design and cost estimation is used. The algorithm implements strength and serviceability limits and the building type requirements defined by the IBC. The major system components and design choices that significantly affect cost are found and discussed.
    • Studies of elves and their connection to lightning with the Pierre Auger Observatory

      Wiencke, Lawrence; Merenda, Kevin-Druis; Sarazin, Frederic; Carr, Lincoln D.; Marshall, Robert; Abbud-Madrid, Angel (Colorado School of Mines. Arthur Lakes Library, 2020)
      Emissions of Light and Very-low frequency perturbations due to Electromagnetic pulse Sources (elves) are observed by the Pierre Auger Cosmic-Ray Observatory (Auger), located in Malargüe, Argentina, with an unprecedented acquisition rate of 10 MHz. An elve is a ring-shaped transient luminous event that expands across the base of the ionosphere at 90 km altitude, above thunderstorms. The elve-observation footprint of the Auger Fluorescence Detector (FD) is 3×10^6 km2, extending over this region known for the highest lightning-flash rate in the tallest thunderstorms on Earth. Northern Argentina has also be identified as one of the only landmasses struck by lightning superbolts, which radiate more than 1 MJ in the form of an electromagnetic pulse. In this dissertation, I first provide background on thunderstorm electrification, lightning processes, and transient luminous events. Second, I present phenomenological properties that I reconstruct directly from the elve data of the Auger FD. I report the first observation of an elve with a complex light spectrum and an elve with a record radial extent of 1000 km. I also reconstruct the lowest altitude intra-cloud lightning stroke ever reported from the observation of elves, 7 km. Third, I detail the end-to-end simulation and perform sensitivity studies of the simulation of the photon surface density of elves to various lightning properties. I employ the elve simulation to estimate the sensitivity of the Auger FD to the altitude of lightning strokes. Fourth, I compare the simulation directly to two well-characterized elves acquired by the Auger FD to assess the validity of the end-to-end simulation. The detailed comparison of well-calibrated data and elaborate simulation will guide future improvements in the current models used to describe elves. From the simulation, I parametrize a relationship between lightning peak current and elve maximum brightness to reconstruct the lightning current of the Auger elve-inducing lightning strokes. Finally, I summarize the major results of this work and how they benefit the field of atmospheric electricity physics.
    • Critical analysis of a practical fourth order finite-difference time-domain algorithm for the solution of Maxwell's equations

      Elsherbeni, Atef Z.; Thomson, Antonio P.; Aaen, Peter H.; Hadi, Mohammed (Colorado School of Mines. Arthur Lakes Library, 2020)
      The finite-difference time-domain (FDTD) method is a highly effective numerical method of solvingMaxwell's equations in the time domain. Traditionally the approximation of the derivatives in Maxwell's equations is based on a central differencing scheme which is second order accurate (second order). The high complexity of today's electromagnetic problems necessitate a FDTD formulation that can use less computational memory and complete simulations faster than current second order FDTD formulations. Many researchers have studied the benefits of FDTD formulations based on fourth order approximations of the spatial derivatives (fourth order). However, none has presented a complete non-specialized case that leads to the simulation of practical antenna or electromagnetic problems. For this reason, and due to the complexity of the available fourth order formulations and the lack of comprehensive analysis of such FDTD formulations, none of the existing commercial electromagnetic software packages use any fourth order FDTD formulations for solving practical problems. The goal of this thesis is to implement, validate, and provide performance analysis of a practical FDTD scheme using fourth order accurate central differencing derivative approximations in space and second order accurate central differencing derivative approximations in time. The simplicity of the fourth order formulation presented in this thesis comes from that fact that it is derived from Taylor series expansions of a general function. The formulation of the FDTD updating equations is developed for general mediums as well as lumped circuit elements (voltage sources, resistors, capacitors, inductors, and diodes). Additionally, updating equations for fourth order convolutional perfectly matched layers (CPML) are derived. This formulation is straightforward, advantageous, and provides a practical fourth order FDTD formulation for electromagnetics applications. Verification and simulation accuracy of the developed fourth order formulation are confirmed through the application of Gaussian propagation, a cavity resonator, the radiation from a dipole antenna, antenna arrays, and the radar cross section calculation of a dielectric cube. Simulations of discontinuous boundaries are also explored in detail through the simulation of PEC objects and high permittivity objects. Various different methods of special fourth order updating equations are thoroughly tested at these boundaries and the results are analyzed. The computational advantages of the developed fourth order FDTD formulation are explored and results show reduced memory usage up to a factor of 6.97 and reduced simulation time up to a factor of 8.70 compared to the traditional second order FDTD formulation.